The Company for Space and Development who provide spacecrafts, fighters and that kind of stuff needed someone well-trained and obedient, who was non-loyal to any army.
Then, they started to train their own pilots.

After a few years, they realized that no others knew better their 'products' like their pilots.
So they started to train elite troops for hire -mercenaries- and one of the division of this mercenaries were the 'Assault Astronauts'.

They fight in the Outer Space battles, where a high knowledge of the Space is needed to survive.
Armored with railguns -'cause there is no air for explosions in the Space -and chainsaws, they break into the enemy ship and try to get the control of it.